Optimization of organics to nutrients (COD:N:P) ratio for aerobic granular sludge treating high-strength organic wastewater

Rania Ahmed Hamza; Mohamed Sherif Zaghloul; Oliver Terna Iorhemen; Zhiya Sheng; Joo Hwa Tay

doi:10.1016/j.scitotenv.2018.10.026

Optimization of organics to nutrients (COD:N:P) ratio for aerobic granular sludge treating high-strength organic wastewater

Sci Total Environ. 2019 Feb 10;650(Pt 2):3168-3179. doi: 10.1016/j.scitotenv.2018.10.026. Epub 2018 Oct 4.

Authors

Rania Ahmed Hamza¹, Mohamed Sherif Zaghloul², Oliver Terna Iorhemen², Zhiya Sheng², Joo Hwa Tay²

Affiliations

¹ Department of Civil Engineering, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada. Electronic address: rania.sayedeid@ucalgary.ca.
² Department of Civil Engineering, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada.

PMID: 30373093
DOI: 10.1016/j.scitotenv.2018.10.026

Abstract

The present study attempted to optimize the nutrients required for biological growth and biomass synthesis in the treatment of high-strength organics wastewater using aerobic granular sludge (AGS). Three identical sequencing batch reactors (SBRs) were used to cultivate aerobic granules at COD concentration of ~5000 mg/L at COD:N:P ratios of 100:2.8:0.4, 100:4.4:0.5, and 100:5:0.7. Results indicated that the amount of nutrients needed for biomass growth does not follow the conventional organics to nutrients ratio (COD:N:P) of 100:5:1 when dealing with high-strength organics wastewater. The highest removal efficiency was achieved at COD:N:P ratio of 100:2.8:0.4, where COD, TN, and P removal was 98.8 ± 0.3%, 100.0 ± 0.0%, and 99.3 ± 1.0%, respectively. Moreover, the presence of high amounts of organics led to the dominance of the fast-growing heterotrophs in all SBRs, with the genus Thauera identified as the most abundant genera (23-40%), while autotrophic nitrifiers disappeared. The observed biomass yield at COD:N ratio of 100:2.8 suggested that heterotrophic nitrification may have occurred, while at COD:N ratios of 100:4.4 and 100:5, all the nitrogen was used for biomass synthesis. Moreover, at COD:N ratio of 100:5, almost 1/5 of the organics were utilized by the biomass cells to produce EPS as defensive action against the effects of free ammonia. Batch optimization experiments showed that the fastest rate of removal occurred at COD:N:P ratio of 100:1.1:0.4. After 4 h, the COD, TN, and P removal efficiencies were 95%, 99%, and 96%, achieving overall removal efficiencies of 98%, 100%, and 97% respectively, at HRT of 8 h. The bacterial behavior in consuming the organics was altered under nutrient-deficient conditions, where faster degradation rates were observed as the amounts of nutrients decreased, with higher relative abundance of heterotrophs and diazotrophic bacterial populations.

Keywords: Aerobic granular sludge; Biomass growth; COD:N:P ratio; High-strength organic wastewater; Microbial community; Nutrients requirements.